Fuel tank construction



April 1952 w. c. BOMHARDT EI'AL. 2,591,044

FUEL TANK CONSTRUCTION Filed 001:. 26, 1945 VII/M 1N VEN TOR. WAR/PEN 6.BOMHAl-POT EARL H. 50/?6 A TTOR/VEY Patented Apr. 1, 1952 FUEL TANKCONSTRUCTION Warren 0. Bomhardt, Baltimore, and Earl H. Sorg, Hyde, Md.,assignors to The Glen L. Martin Company, Middle River, Md., acorporation of Maryland Application October 26, 1945, Serial No. 624,756

4 Claims.

This invention relates to an integral tank structure for the storage ofliquids and more particularly relates to a structure for rendering theseams of integral tanks fluid-tight for hydrocarbon liquids, yet remainssufficiently flexible so that the liquid will not seep through the seamsupon repeated deflection of the structure.

The efficient storage of liquid fuel and oil, particularly in aircraft,presents somewhat of a problem. It is most desirable to utilize space inaircraft that is not particularly useful for other purposes for thestorage of fuel and lubricating oil. The space in the wings between thefront and rear spars and adjacent ribs is usually employed for thestorage of fuel and oil. In seaplanes the portion of the hull under thefloor is fitted and used for storage purposes. Due to the fact that theconstruction of the hull and the wings of airplanes are light weightriveted aluminum structures, it has been difficult to fabricate anintegral tank and depend upon sealing the riveted joints adequately tohold fuel. Many attempts have been made to coat seams with fillers andsealing compounds and to place caulking strips in the riveting joints.Special sealing and treatment of the rivets has also been resorted towith only temporary success. The problem of storing hydrocarbon liquidsin aircraft was successfully solved by use of the Mareng cell, describedin the Gray and Zivi Patent 2,102,590, issued December 21, 1937. Thispatent relied upon a bag or cell placed in the cavity to be used for thestorage of fuel, the dimensions of which were substantially equal to thecavity so that the cell acted as a containing structure, while thecavity walls bore the fluid pressure load of the liquid in the bag orcell. This construction solved the problem of storing fuel in cavitiesin aircraft that has been universally adopted for this purpose. Whilethe cell wall is thin, it has a certain volumetric capacity andtherefore takes up some of the space that might be used for the storageof fuel as well as adds to the dead-load weight of the airplane. Thestructural deflection of the aircraft in flight could not cause leakageor seepage of the fuel.

While the above solution has been quite satisfactory, it is stilldesirable to store fuel in integral tanks if some method or means can bedevised to seal the seams of the tanks against leakage when the seamsare stressed by the deflection of the structure.

It is an object of this invention to provide a material to be used as acaulking strip in the seams of integral tanks, which material has apredetermined degree of swelling when in contact with hydrocarbon liquidso that the material on the inner edge of the seam near the hydrocarbonliquid will be caused to swell a controlled amount to keep the space inthe riveted joint fluid-tight at all times.

Further and other objects will become apparent from the description ofthe accompanying drawings which form a part of this disclosure and inwhich like numerals refer to like parts.

In the drawings:

Figure 1 is a fragmentary view of a portion of a seaplane hull embodyingthe invention.

Figure 2 is a section taken on the line 2--2 of Figure 1.

The side walls of a seaplane hull in Figure 1 are shown at 3 with thebottom walls 4 sloping down to the keel 5 from the chines 6. A space inthe bottom of the seaplane hull underneath the floor I is usuallyutilized for the storage of fuel and oil. This space may be divided bypartitions such as 8 into compartments. The usual construction of such ahull involves riveted joints which have in the past been as carefullysealed and caulked as possible but still were not sufficiently tightwhen the structure was stressed so that they could be used for thestorage of fuel without covering the lon eron 9 and ribs ID to permitthe insertion of a Mareng cell. In order to make the cavities in aseaplane hull formed as described above, suitable for the storage offuel, it is merely necessary to incorporate in each riveted joint asshown in Figure 2 sealing strips such as I I or I2 made in accordancewith this invention. The single riveted joint l3 will be renderedfluid-tight by reason of the strips ll placed between rib l0 and sidewall 3. At a double riveted lap joint such as [4, it will be necessaryto employ in addition to sealing strip H, a second sealing strip 12.

It is usual in attaching the skin on the frame of a seaplane to placethe skin on the frame during the process of drilling the rivet holes.After all of the holes are drilled and prior to riveting, sealing stripsII and 12 are put in place and a hot instrument run through the rivetholes will puncture the sealing strip used. It is possible but not aspractical to drill the skin and ribs with the sealing strip in place.

The advantage of the particular tape employed in this invention isderived from its composition. A vinyl resin compound is employed for thepurpose that eXhibits flexibility and swelling characteristics in fuel,particularly in the aromatic blended fuels. The swelling characteristicis of a controlled degree so that that portion of the tape in contactwith the fuel swells to make the joint fluid-tight. If, after continuousflexing, the seam permits the seepage of fuel further than the initialswelled portion of the tape, further swelling of the tape will takeplace as the fuel seeps along the seam to render the seam fluid-tight.There are many materials that exhibit a swelling characteristic whenimmersed in such hydrocarbon liquids but the degree of swelling isusually uncontrolled. Either excessive swelling will take place orswelling not great enough to produce the desired results for the purposeof this invention. Most of the materials that do swell when in contactwith these hydrocarbon liquids become soft and weak or hard and brittlewhich renders them unsatisfactory for repeated exthat would render themsuitable for the purpose of practicing this invention. Synthetic resinelastomeric materials swell to various degrees in aromatic blended fuelsbut the softeners incorporated in their compounds are either extractedby the action of the fuels rendering them hard and brittle or the resinsdo not exhibit the desired swelling characteristics. The gasket materialemployed in this invention is obtained by milling a composition of 70%of a material known as VYNW and 30% of material known as Paraplex G-25and then molding or extruding the stock into the desired gage and shape.The material known as VYNW is a copolymer of 93- .95% vinyl chloride and7-5% vinyl acetate. The material known as Paraplex G-25 is a poly esterof glycol sebacate.

If it is desired touse this material as a coating for fabrics, it can bemade up in a solution consisting of il VYNW, 4.9% Paraplex G-25, 32.6%cyclohexanone and 51% methyl ethyl ketone. This solution may be appliedas a coating to a fabric such as thin cotton flannel until a totalthickness of approximately .045" to .050" is obtained after-theevaporation. Such fabric can be readily coated with this material by thecustomary calendering process. This formulation can also be extruded orcast into a film of any desirable thickness and used as outlined above.When the solvent evaporates from the above solution, theresulting'material-will be approximately 70% VYNW and 30% ParaplexG-ZS.

The sealing material made in the manner described above has a very lowcoldflow characteristic, that is, that when distorted by the pressureinvolved in the riveting operation of the Joint it tends to remainintact and resist the pressure and maintain its shape rather than oozeout of the crevices and cracks under pressure. The material can be madeinto a strip having smooth surfaces that form a good seal with the sheelmetal being riveted.

The swelling characteristic of the -material used as a seal in the jointof a structure is the most important feature. The composition of matterdescribed above when extruded or cast into a thin strip or film, whenimmersed in ordinary aromatic aviation fuel which is a 40% aromaticfluid with 60% 100 octane gasoline; will exhibit the swellingcharacteristic of up to about 36%, When the material is in the seam of ariveted joint only the'edge in contact with the fuel will swell and asthe seam opens up and fuel seeps in, the material will swell to stop theseepage of fuel into the seam. When the fuel is removed from the scam,the tape resumes its normal volume.

It will be rare in use that the material will be required to swell toits full amount of 36% but it will always be some lesser amount. Whenthe composition is made up with cyclohexanone and methyl ethyl ketone assolvents and used as a coating on flannel or fabric, the swelling isheld In other words, the swelling is In some to about 15%. restrained bythe reinforcing fabric.

. installations the reinforced coated tape may be desirable Where onlylimited degrees of swelling will be required, but for maximum sealing,the cast or extruded form of tape within the reinforced fabric is mostdesirable.

' It is to be understood that certain changes,

alterations, modifications and substitutions can be made'withoutdeparting from the spirit and scope of the appended claims.

We claim as our invention:

1. A tank for the storage of hydrocarbon liquidshaving its structuralmembers secured together by a plurality of rivets, a sealing stripinserted in each joint between said members, said rivets extendingthrough said members and said sealing strip, said strip comprising acomposition of substantially 70% of copolymer of about 06% vinylchloride and 4% vinyl acetate and of a poly ester of glycol sebacate.

2. A tank for the storage of hydrocarbon liquids having its structuralmembers secured together by a plurality of rivets, a sealing stripinserted in each joint between said members, said rivets extendingthrough said members and said sealing strip, said strip comprising acomposition of vinyl chloride and vinyl acetate, with a poly ester ofglycol sebacate which exhibits a swelling characteristic of about 36%when immersed in aromatic fuel.

3. A tank forthe storage of hydrocarbon liq- .uids having its structuralmembers secured together by a plurality of rivets, a sealing stripinserted in each joint between said members, said rivets extendingthrough said members and said sealing strip, said strip comprising astrip of fabric impregnated with a composition of substantially of acopolymer of about 96% vinyl chloride and 4% vinyl acetate, and 30% of apoly ester of glycol sebacate.

4. 'A tank for the storage of hydrocarbon liquids having its structuralmembers secured together by a plurality of rivets, a sealing stripinserted in each joint between said members, said rivets extendingthrough said members and said sealing strip, said strip comprising astrip of fabric impregnated with a composition of vinyl chloride andvinyl acetate, with a poly ester of glycol sebacate which exhibits aswelling characteristic. of about 36% when immersed in aromatic fuel.

WARREN C. BOMHARDT. EARL H. SORG.

REFERENCES CITED -The following references are of record in the file ofthis'patent:

UNITED STATES PATENTS Number Name Date 2,140,672 Gray et a1. Dec. 20,1938 FOREIGN PATENTS Number Country Date 523,247 Great Britain July 10,1940 OTHER REFERENCES Fligor et al.,'Resinous Plasticizers from SebacicAcid, Ind. and Chem. Eng. 37 (5), pp. 504-508, May 1945.

Chem. and Eng. News, Dec. 10, 1944, page 2115.

The Resinous Reporter, February 1944, page 8.

The Resinous Reporter, July 1944, pages 6-8.

1. A TANK FOR THE STORAGE OF HYDROCARBON LIQUIDS HAVING ITS STRUCTURALMEMBERS SECURED TOGETHER BY A PLURALITY OF RIVETS, A SEALING STRIPINSERTED IN EACH JOINT BETWEEN SAID MEMBERS, SAID RIVETS EXTENDINGTHROUGH SAID MEMBERS AND SAID SEALING STRIP, SAID STRIP COMPRISING ACOMPOSI96% OF VINYL CHLORIDE AND 4% VINYL ACETATE AND 30% OF A POLYESTER OF GLYCOL SEBACATE.